1. Field of the Invention
The present invention relates to an opto-electric hybrid module in which an optical waveguide and an electric circuit with an optical element mounted thereon are combined, and to a manufacturing method thereof.
2. Description of the Related Art
An opto-electric hybrid module is manufactured, for example, as shown in FIG. 9, by preparing an electric circuit board E and an optical waveguide W0 individually, bonding both to each other with an adhesive 5, and then mounting a light-emitting element 11 and a light-receiving element 12 on portions of the above-mentioned electric circuit board E corresponding to opposite end portions of the above-mentioned optical waveguide W0 (see, for example, Japanese Patent Application Laid-Open No. 2004-302345).
The above-mentioned electric circuit board E is constructed such that an electric circuit 3 is formed on the surface of a stainless steel substrate 1, with an insulation layer 2 therebetween. Portions of this electric circuit 3 serve as mounting pads 3a for mounting the above-mentioned light-emitting element 11 and light-receiving element 12 thereon. The above-mentioned optical waveguide W0 is constructed such that an under cladding layer 86, a core 87, and an over cladding layer 88 are formed in the order named from the back side of the above-mentioned stainless steel substrate 1. Further, V-shaped notches are formed in portions near the opposite ends of the above-mentioned optical waveguide W0. One side surface of the V-shape is formed as an inclined surface inclined at 45 degrees to the above-mentioned electric circuit board E, and an end portion of the core 87 positioned at the inclined surface serves as an optical path conversion mirror 87a. In this opto-electric hybrid module, the above-mentioned electric circuit board E has a through hole 4 for light propagation formed on the light-emitting element 11 side thereof so as to enable light beams (an optical signal) L emitted from the light-emitting element 11 to enter the end portion of the core 87 on the light-emitting element 11 side. Also, the above-mentioned electric circuit board E further has a through hole 4 for light propagation formed on the light-receiving element 12 side thereof so as to enable the light-receiving element 12 to receive the light beams L emitted from the light-emitting element 11 and coming through the core 87 of the optical waveguide W0 to the optical path conversion mirror 87a on the light-receiving element 12 side. In FIG. 9, the reference character 11a designates a light-emitting portion of the above-mentioned light-emitting element 11, and the reference character 11b designates a bump (electrode) of the light-emitting element 11. Also, the reference character 12a designates a light-receiving portion of the above-mentioned light-receiving element 12, and the reference character 12b designates a bump (electrode) of the light-receiving element 12.
The propagation of the light beams L in the above-mentioned opto-electric hybrid module is accomplished in a manner to be described below. First, the light beams L are emitted downwardly from the light-emitting portion 11a of the light-emitting element 11. The light beams L pass through the through hole 4 for light propagation of the electric circuit board E and then through the under cladding layer 86 in a first end portion (a left-hand end portion in FIG. 9) of the optical waveguide W0, and enter a first end portion of the core 87. Subsequently, the light beams L are reflected from the optical path conversion mirror 87a provided in the first end portion of the core 87 (or the optical path is changed by 90 degrees), and travel through the interior of the core 87 in an axial direction. Then, the light beams L travel through the interior of the core 87 and a repropagated to a second end portion (a right-hand end portion in FIG. 9) of the core 87. Subsequently, the light beams L are reflected upwardly from the optical path conversion mirror 87a provided in the above-mentioned second end portion (or the optical path is changed by 90 degrees), pass through and exit from the under cladding layer 86, and are received by the light-receiving portion 12a of the light-receiving element 12.
However, the light beams L emitted from the light-emitting portion 11a of the above-mentioned light-emitting element 11 are diffused, as shown in FIG. 9. Thus, if the distance between the light-emitting element 11 and the optical path conversion mirror 87a provided in the first end portion of the core 87 is long, the light beams L deviate from the optical path conversion mirror 87a and are not guided into the core 87 in some instances. Similarly, the light beams L reflected from the optical path conversion mirror 87a provided in the second end portion of the core 87 are also diffused. Thus, the light beams L deviate from the light-receiving portion 12a of the light-receiving element 12 and are not received by the light-receiving portion 12a in some instances. For these reasons, there is a problem with the prior art opto-electric hybrid module in that the propagation loss of the light beams L is increased.
During the mounting of the light-emitting element 11 and the light-receiving element 12 in the manufacture of the above-mentioned opto-electric hybrid module, the positions of the optical path conversion mirrors 87a provided in the opposite end portions of the core 87 are in general recognized through the through holes 4 for light propagation formed in the above-mentioned electric circuit board E by using an image recognition apparatus and the like, whereby the mounting positions are identified. To this end, it is necessary that the optical waveguide W0 is already formed during the mounting of the above-mentioned light-emitting element 11 and the like. On the other hand, during the mounting of the above-mentioned light-emitting element 11 and the like, the bump 11b thereof is heated to melt (at approximately 230 to 250° C.), and is then connected to the mounting pads 3a of the electric circuit 3. For this reason, the heating during the mounting of the above-mentioned light-emitting element 11 and the like causes thermal stresses to act on the optical waveguide W0, thereby distorting the optical waveguide W0. As a result, this decreases the accuracy of alignment (positioning) of the light-emitting element 11 and the like with (relative to) the optical path conversion mirrors 87a provided in the opposite end portions of the core 87 to result in the increase in the propagation loss of the light beams L.